We are conducting a scientific campaign from the Arecibo Observatory to observe red dwarf star with planets. These observations might provide information about the radiation and magnetic environment around these stars or even hint the presence of new sub-stellar objects including planets. So far, we observed Gliese 436, Ross 128, Wolf 359, HD 95735, BD +202465, V* RY Sex, and K2-18. Only Gliese 436 and K2-18 are known to have planets. Observations were done between April and May 2017 in the C-band (4 to 5 GHz).

Two weeks after these observations, we realized that there were some very peculiar signals in the 10-minute dynamic spectrum that we obtained from Ross 128 (GJ 447), observed May 12 at 8:53 PM AST (2017/05/13 00:53:55 UTC). The signals consisted of broadband quasi-periodic non-polarized pulses with very strong dispersion-like features. We believe that the signals are not local radio frequency interferences (RFI) since they are unique to Ross 128 and observations of other stars immediately before and after did not show anything similar.

We do not know the origin of these signals but there are three main possible explanations: they could be (1) emissions from Ross 128 similar to Type II solar flares, (2) emissions from another object in the field of view of Ross 128, or just (3) burst from a high orbit satellite since low orbit satellites are quick to move out of the field of view. The signals are probably too dim for other radio telescopes in the world and FAST is currently under calibration.

Each of the possible explanations has their own problems. For example, Type II solar flares occur at much lower frequencies and the dispersion suggests a much farther source or a dense electron field (e.g. the stellar atmosphere?). Also, there are no many nearby objects in the field of view of Ross 128 and we have never seen satellites emit bursts like that, which were common in our other star observations. In case you are wondering, the recurrent aliens hypothesis is at the bottom of many other better explanations.

Therefore, we have a mystery here and the three main explanations are as good as any at this moment. Fortunately, we obtained more time to observe Ross 128 next Sunday, July 16, and we might clarify soon the nature of its radio emissions, but there are no guarantees. We will also observe Barnard’s star that day to collaborate with the Red Dots project. Results from our observations will be presented later that week. I have a Piña Colada ready to celebrate if the signals result to be astronomical in nature.

UPDATE 2017/07/17: We successfully observed Ross 128 last night from the Arecibo Observatory. It was raining during the observations but this has a minimal effect on the C-band. SETI Berkeley with the Green Bank Telescope and SETI Institute's ATA joined our observations. We need to get all the data from the other partner observatories to put all things together for a conclusion. Probably by the end of this week.

UPDATE 2017/07/19: We have all the Arecibo data ready to analyze. We are still waiting for the data from the other partner observatories to present a conclusion probably on Friday. This excellent article by Sarah Kaplan gives a personal perspective on this issue.

UPDATE 2017/07/20: The @BerkeleySETI team released an analysis of @GrnBnkTelescope #Listen observations of the star #Ross128 after claim of a possible signal.

Abel Mendezabel.mendez@upr.eduross12815https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/47585213230601493062017-07-15T22:58:29.626Z2017-07-17T19:53:27.259Z2017-07-17T19:53:25.668ZObservations of Barnard's Star and Ross 128 for Sunday, July 16

Figure Above: Sample data for Gliese 436

Introduction

Eight telescope in the world will join efforts on Sunday, July 16, to observe two red dwarf stars, Barnard's Star and Ross 128. Here are the details of the Arecibo Observatory's plans.

General Observation Protocol for Arecibo's Observations

We are measuring radio flux density at frequencies within the C-band 4 to 5 GHz (1 GHz bandwidth) with roughly a frequency resolution of 21 kHz and time resolution of 0.1 seconds. Beam size (field of view) at these frequencies is about 1.0 x 0.9 arcmin.

The typical observation session consists of blocks of 10 minutes ON target followed by 10 seconds ON/OFF diode calibration. Data is recorded using CIMA and analyzed with a custom IDL code (see figure above for sample data product).

The activity of red dwarf stars, such as Proxima Centauri and TRAPPIST-1, are of special interest due to their potential to support habitable planets around them. Planets around these stars could experience tidal locking, strong stellar magnetic fields, strong flares and high UV and X-ray fluxes, all factors that might affect their habitability. Red dwarf stars are also known emitters of radio-flaring emissions near 5 GHz that are not always correlated with other spectral emissions. We hypothesize that periodic interaction of close-in planets with the magnetosphere of the star might produce small but detectable effects on the occurrence or shape of their radio emissions. Here we used the Arecibo Observatory to observed at 4 to 5 GHz (C-band) the red dwarf star Gliese 436. This star is not a known emitter of radio flares but has a close-in hot-neptune planet in an elliptical orbit. Our goal was to characterize its radio emissions and search for any potential correlations between its activity and the presence of its planet. For comparisons, we observed the six known flare stars Ross 128, Wolf 359, HD 95735, BD +202465, and V* RY Sex. We also observed K2-18, a red dwarf star with an Earth-sized planet in the habitable zone. Radio flux calibration was done with the quasar 3C263.1 (B1140+223). We are currently analyzing over 200 Gb of data from these observations.

Abel Mendezabel.mendez@upr.eduresearchopportunitiesforundergraduates20175https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/59172034880430081972016-12-30T20:33:33.033Z2016-12-30T20:35:57.860Z2016-12-30T20:35:55.552Z25 Years of Exoplanet Discoveries

The pulsar planets have been detected orbiting PSR B1257+12, the 6.2-millisecond pulsar discovered in February 1990, during a survey of the radio sky with the 305-m Arecibo radio telescope. The two outer planets, announced in January 1992, have masses of about 4 times the mass of our Earth, and the inner one, detected in 1994, is only twice as massive as the Moon. The corresponding orbital periods of the three planets are 98, 65 and 25 days. The whole system is compact enough to fit inside the orbit of Mercury.

The pulsar planet discovery has been made using the highly precise pulse timing technique. It was possible because the orbiting planets make the pulsar wobble in space, and that motion translates into easily measurable, millisecond variations in the pulse arrival times at the telescope. The same technique was used to confirm the existence of the pulsar planets by detecting subtle changes in the orbits of the two larger planets caused by their proximity to the 3:2 orbital resonance.

A planetary system orbiting PSR B1257+12 represents the first confirmed planets beyond the Sun. It is also the first extrasolar planetary system, in which an orbital resonance has been measured, and it is the first example of a “tightly packed”, super-Earth mass system, which is the kind of orbital configuration now commonly detected by the Kepler telescope and the most sensitive radial velocity surveys. From the very start, the existence of such a system carried with it a prediction that planets around other stars must be common, and that they may exist in a wide variety of architectures, which would be impossible to anticipate on the basis of our knowledge of the Solar System alone.

The PHL @ UPR Arecibo has an exoplanets session on Connecting Habitability and Biosignature Observations as part of the AbSciCon 2017, April 24-28, 2017 in Mesa, Arizona. The session is organized by Abel Méndez (PHL @ UPR Arecibo), Dirk Schulze-Makuch (Washington State University), and Edgard Rivera-Valentin (Arecibo Observatory/USRA).Here are the abstract submission instructions (Deadline: January 18, 2017). There is also a related workshop on quantitative measures of habitabilityon February 2017 in Puerto Rico.

Summary: On Earth, habitability is generally correlated with the presence of life, but this will not necessarily be the case for all habitable planets. For instance, a biosignature on a non-habitable planet by terrestrial standards could be interpreted as a false-positive or caused by very different biological process, among other explanations. Therefore, it is necessary to include quantitative measures of habitability to properly assess the significance of any biosignature detections. This session is requesting presentations about potential correlations between habitability and biosignature observations based on theoretical or empirical models, including those for complex or exotic life forms. The models presented as part of this session might consider any spatial and temporal scale, and extend from microbial to complex life, but should address how these models might scale-up and produce together both detectable global habitable conditions and biosignatures from afar.

What does it take to consider a planet potentially habitable? If a planet is suitable for life, could life be present? Is life on other planets inevitable? Searching for Habitable Worlds answers these questions and provides both the general public and astronomy enthusiasts with a richly illustrated discussion of the most current knowledge regarding the search for extrasolar planets. Nearly everyone wants to know if we are alone in the universe. This book might not have the answers, but shows where we should look.

This book is a fun and accessible book for everyone from middle schoolers to amateur astronomers of all ages. The use of non-technical language and abundant illustrations make this a quick read to inform everyone about the latest movement in the search for other planets that we might be able to inhabit. After a brief discussion on why humans are hard-wired to be curious, and to explore the unknown, the book describes what extrasolar planets are, how to detect them, and how to pin down potential targets. In addition, a data-driven list of the best candidates for habitability is profiled and the next generation of exoplanet-hunting scientific instruments and probes are identified.

Abel Mendez is an Associate Professor of Physics and Director of the Planetary Habitability Laboratory, Department of Physics and Chemistry, University of Puerto Rico at Arecibo, Puerto Rico. He does research about planetary habitability, exoplanets, and astrobiology in general. He is also the creator of the Habitable Exoplanets Catalog.

Wilson Gonzalez-Espada is an Associate Professor of Physics and Science Education, Department of Mathematics and Physics, Morehead State University, Morehead, Kentucky. His scholarly interests include science communication, the public understanding of science, and physics education research. He is also one of the editors of the book Ciencia Boricua.

Abel Mendezabel.mendez@upr.edushw8https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/72806389186119092442014-07-08T17:45:46.251Z2016-08-24T16:48:50.890Z2015-01-09T15:30:58.748ZWhat is habitability and how is it measured?

Not everywhere on Earth is equally habitable. From deserts to rain forest there is an obvious habitability gradient, from worst to best for life. We are using the presence of life as a ‘proxy for habitability’ to recognize similar pattern, assuming that a place with more life is more habitable than the other, an assumption not always correct. This type of patterns helps to correlate what environmental factors control conditions which support the presence of more life. Scientists use this type of information to create models to predict from the environment how much life they can potentially support.

A habitable environment is just an environment that might support some form of life, not necessarily one with life. Earth today is not that good for life if we consider its extensive areas of dry and cold deserts compared to rain forests. Mars is a certainly a desert planet but Earth today is more like a dry forest planet, on average. Imagine a rain forest planet, where most of its land areas support abundance life. That will be more habitable than Earth, again using the abundance for life as a proxy for habitability.

How exactly do we measure or quantify habitability? Habitability metrics is an emerging field within astrobiology, or more correctly a re-emerging field since the basis for it were established more than three decades ago. One of the most frequent questions in the astrobiology field is how to measure habitability. Some people even take the concept as difficult to define as life. The true is that biologists already tackled this problem successfully during the ’70 and ’80 but is still seldom known by the astrobiology community. There are various reasons for this.

First, habitability metrics originated within the field of ecology and population dynamics to understand the distribution of wild animals and plants. This seems to have no relation to astrobiology since it focuses more on microbial life. Second, this is a very specialized field within theoretical ecology and even not taught and used by all ecologists. Third, biologist calls it differently. We use the generic word ‘habitability’ but it is formally called ‘habitat suitability’ by biologists. So if an astrobiologist tries to look for scientific references on how to measure habitability he/she would probably miss the ‘habitat suitability’ concept or seem as irrelevant since it focus now on animal and plant life.

The definition and core mathematical framework of ‘habitat suitability models’ is something that can be extended to all forms of life, including microbial life, and to the astrobiology field. That is precisely one of the reason we established the Planetary Habitability Laboratory on 2010, to adapt and apply this framework to the astrobiology field, as we call it ‘habitability metrics for astrobiology.’ Our first application was the Earth Similarity Index (ESI), a measure of Earth-likeness for planets based on a given set of planetary parameters. This index was inspired by the diversity and similarity indices used in ecology to compare populations. Similarity indices are also used in many other applications such as pattern recognition (e.g. face recognition). Still, this approach is an indirect measure of habitability and we want more direct measures.

Habitability or ‘habitat suitability’ is defined as the suitability of an environment for life. This definition has three components, an environment, a life, and a suitability (see figure). All three need to be defined for a proper assessment of habitability. The ‘environment component’ is a description of the physical, chemical, or even biological location of life under consideration, the habitat. It is constrained by some space and time limits (e.g. surface of Earth today). This is the astronomy, planetary science, or geology part of the metric. The other two components contain the biology. The ‘life components’ requires the selection and knowledge of an individual species or community (i.e. aggregate of two or more species) as the test subject for the habitat. Therefore, given some habitat any habitability measure is always relative to the species or community under consideration. Finally, the ‘suitability component’ is the tricky part because it defines the connection between the environment and life. This is the ‘proxy for habitability’.

The suitability for life, or ‘proxy for habitability’, could be direct or indirect. An indirect suitability does not necessarily specify how exactly the environment component affects life. For example, we know that the environment requires liquid water but we don’t care about the specific differences on the quantity or quality of this water for life (e.g. salinity, temperature). This is the case of current efforts searching for habitable environments in planetary environments such as exoplanets. The occurrence of Earth-size planets in the habitable zone of stars (Eta-Earth) is in fact an indirect measure of stellar habitability, the suitability of stars for planets with life. The ESI is also an indirect measure, but of planetary habitability, the suitability of a planet for Earth-like life. Thus, indirect measures of habitability rely on occurrences (aka presence/absent in biology), a similarity, or probability of some necessary conditions for life. It is recommended that these values be expressed with a common scale as a fraction for consistency, where zero denotes a non-habitable environment and one denotes a highly habitable environment. Negative values could be used to rate the magnitude of the damaging effect of a non-habitable environment (e.g. both the surface of Mars and Venus are non-habitable, but Venus is worst). Values over one could represent super-habitable conditions.

The hardest part is to define direct measures of habitability, which are more biologically meaningful. These require much more knowledge of the interaction of life and the environment. There are some specific universal biological quantities that can be used as the ‘proxy for habitability’ such as growth rate, carrying capacity, metabolic rate, or productivity. Therefore, to construct a direct measure of habitability requires knowing how the environment affects one of these biological quantities for some species or community. We don't need to specifically estimate these quantities but only how the environment proportionally affects them. For example, we know how temperature affects the productivity of primary producers such as plants and phytoplankton. Most require temperatures between 0° to 50° C, but they do better (i.e. highest productivity) near 25°C. Their ‘thermal habitability function’ looks like a bell-shaped curve centered at their optimum productivity temperature. Direct measures of habitability are also better represented as a fraction from zero to one.

Another problem is how to combine the effect of many environmental variables into a single direct or indirect habitability index. These are called aggregation methods in theoretical ecology. There are many ways to do this. Probabilities are simple to combine since they are multiply to each other. Similarity indices are easier to construct and combine too. The use of any direct methods already defines how the environmental variables are combined since they are based on biophysical principles. In practice, we recommend biological productivity as the best ‘habitability proxy’ since we know how to calculate it for microbial to complex life, it is relatively easy to measure or estimate, and there are even ways to measure it via remote sensors. The NASA’s Terrestrial Ecology Program uses the TERRA and AQUA satellites to monitor the global land and ocean primary productivity of Earth. This is a measure of ‘global health’ or ‘terrestrial habitability’ since primary producers are the base of the food chain.

Unfortunately, most applications of habitability metrics in astrobiology are limited to indirect measures of habitability. This is especially true for exoplanets since we don't have enough information about them to appropriately weight how terrestrial life, life as we know it, could be affected by their planetary environment. There is no single quantitative measure of habitability but a collection of metrics for different types of environments and life. Nevertheless, habitability metrics are easy to compare and combine since they use the same scale and meaning (e.g. a value between zero and one). It doesn't matter the application, everybody would understand the meaning of an environment with habitability close to one. The next logical question after this statement is what are the limits of this value, in other words, what is the environment, reference life, and selected suitability under consideration.

Habitability metrics provide an excellent way to understand and compare habitable environments, and prioritize targets for exploration within Earth, the Solar System, and beyond. Biologists have been using them, as 'habitat suitability models' for more than three decades to understand the distribution of terrestrial complex life from local to global environments. It is only a matter of adapting this mathematical framework to the needs of the astrobiology science.

This is a test of the code for our new Visible Daily-Earth project where we will have a true-color global picture of Earth generated daily from geostationary satellites (Figure 1). These are the only satellites that can take the whole Earth in a single shot, but unfortunately not in true-colors and this will be the tricky part of the project. Here we are showing a black and white test version for May 16, 2012 at five different times corresponding to a nearly full-phase Earth as seen by the satellites on those times (Figure 2).

Figure 1. Diagram showing the relative view area of five geostationary meteorological satellites.

Figure 2. The visible Earth on May 16, 2012 at five different times (UTC). The images are generated starting the day in the Australia zone and as Earth rotates ending in the Pacific. Here are a 4MP and 48MP high resolution versions. CREDIT: PHL @ UPR Arecibo, EUMETSAT, NERC Satellite Receiving Station, University of Dundee.

Abel Mendezabel.mendez@upr.eduvisibledaily-earthmay1620127https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/19351385185774377722011-07-26T21:43:36.457Z2016-08-24T16:48:50.888Z2011-07-29T10:46:26.853ZVegetation, Ice and Deserts of the Paleo-Earth

In our previous post we discussed the distribution of landmasses of the Paleo-Earth. Here we used the Visible Paleo-Earth (VPE) datasets to estimate the global surface coverage of vegetation, ice, and deserts in the last 750 million years, during the Phanerozoic (Figure 1). The vegetation regions were defined as any region with over 25% vegetation cover. Ice covered areas include permanent and mountain ice with over 75% ice cover. Deserts are those regions without ice and with less than 25% vegetation cover. We also included as vegetation cover the potential presence of simple photosynthetic eukaryote biota before the appearance of plants 450 Ma (Strother et al., 2011).

According to this preliminary analysis, Earth landmasses today are covered by about 68% vegetation, 11% ice, and 21% desert (Table 1). However, during the Devonian and Cretaceous vegetation cover reached 95%; Earth was a truly "forest planet." Last global glaciation (Snowball Earth) occurred before the Phanerozoic 650 Ma with over 60% ice cover. Later, and smaller, ice caps included the Ordovician, the Carboniferous-Permian, and today. Interestingly, Earth's today is in a period with the lowest global vegetation cover since the appearance of land plants 450 Ma.

Figure 1. Percent of surface coverage of vegetation, ice, and deserts in the last 750 million years. Dotted line correspond to today values (data shown in Table 1).

Table 1. Percent of surface coverage of vegetation, ice, and deserts in the last 750 million years.

Age(Mya)

Age Name

Vegetation

(%)

Ice

(%)

Desert

(%)

000

Present

68.3

10.7

21.0

020

Early Miocene

81.5

1.7

16.8

035

Late Eocene

84.8

0.9

14.3

050

Early Eocene

88.2

0.8

11.0

065

Late Cretaceous (K-Pg)

88.9

0.2

10.9

090

Late Cretaceous

95.4

0.0

4.6

105

Early Cretaceous

97.2

0.0

2.8

120

Early Cretaceous

95.5

0.0

4.5

150

Late Jurassic

96.0

0.0

4.0

170

Middle Jurassic

89.2

0.0

10.8

200

Late Triassic

82.5

0.0

17.5

220

Late Triassic

83.6

0.0

16.4

240

Middle Triassic

83.3

0.0

16.7

260

Late Permian

78.8

13.1

8.2

280

Early Permian

81.2

9.9

8.9

300

Late Pennsylvanian

77.6

20.1

2.3

340

Middle Mississippian

89.8

7.7

2.5

370

Late Devonian

96.1

0.0

3.9

400

Early Devonian

97.4

0.0

2.6

430

Middle Silurian

94.7

0.0

5.3

440

Early Silurian

78.8

0.0

21.2

450

Late Ordovician

78.7

0.0

21.3

470

Middle Ordovician

58.5

11.6

29.9

500

Late Cambrian

47.0

0.0

53.0

540

Early Cambrian

0.0

0.0

100.0

560

Late Proterozoic

0.4

0.0

99.6

600

Late Proterozoic

0.2

16.2

83.6

660

Precambrian

0.0

63.3

36.7

690

Precambrian

0.0

49.1

50.9

750

Precambrian

0.0

36.6

63.4

References

Abel Mendezabel.mendez@upr.eduvegetationiceanddesertsofthepaleo-earth3https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/46829098887327877912011-03-24T06:54:37.932Z2016-08-24T16:48:50.888Z2011-03-24T10:25:53.623ZUsing REDUCE as a computer algebra system (CAS)

There are many computer algebra systems (CAS) available for doing math intensive operations. I needed one in MacOS and Linux/Unix platforms for complex operations, and potentially in an iPad for quick explorations. I previously used Mathematica, but it is an expensive beast specially for many platforms, and it is still not available for the iPad (WolframAlpha is a temporary solution). The only one matching these requirements is the old, proven, and free REDUCE.

Together with Maxima (commercial version is Macsyma), REDUCE was one of the first computer algebra systems born in the 1960's. It is available for almost any platform including the iPad with the iCAS implementation ($15 from the Apple Store, also available for the iPhone). iCAS does not look as pretty as SpaceTime and PocketCAS but it is based in a proven and mature CAS compatible with many platforms, so I can reuse and not need to relearn a CAS syntax for each platform. REDUCE also uses for plotting the syntax of gnuplot so it will be familiar to those with experience in that package.

Manuals and tutorials are available in the REDUCE Project Homepage, the online manual and this reference are specially useful. Here is an example of using reduce to solve some simple problems with MacOS (Figure 1). REDUCE is called from the command line shell in MacOS and Linux/Unix using $reduce with the IDE and $reduce -w without the IDE.

REDUCE Sample Program

% 3D Plotting;

load_package "gnuplot";

plot( cos(sqrt(x**2 + y**2)), x=(-3 .. 3), y=(-3 .. 3), hidden3d);

% Solving integrals;

int(sin(x)*exp(2*x),x);

% Solving equations;

solve({3x + 5y = -4,2*x + y = -10},{x,y});

% Using fixed precision;

on rounded; precision 30;

(1+sqrt(5))/2;

Figure 1. REDUCE window on MacOS using the included IDE.

Abel Mendezabel.mendez@upr.eduusingreduceasacomputeralgebrasystemcas8https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/83807761369212293252011-12-06T14:28:24.443Z2016-08-24T16:48:50.887Z2012-06-30T18:56:11.438ZUpdates on Kepler-22 b during the First Kepler Science Conference

Dec05: The recent confirmation of Kepler-22 b (KOI-087) does not qualify as a potential habitable exoplanet in the Habitable Exoplanets Catalog. It is in the habitable zone of the star but it is also too big and classified here as a Warm Neptunian. Most of the interesting exoplanets in our catalog are Kepler objects too just waiting for confirmation as Kepler 22b did today.

Dec06: This is our basic habitability analysis for Kepler-22 b. We have conflicting values for the radius (and proposed mass) from various sources (Kepler database have 2.38 Earth Radii) but we will correct this with the paper. In either case the ESI is less than Mars and classified as a Warm Neptunian non-habitable, although very close to a superterran size. "Surface temperature" is good (~40°C) but this is probably the temperature of the top water clouds layers. Venus has nice temperatures in the top clouds layers too, but lead-melting temperatures at the surface. Still, this is an interesting object for future observations. One more thing... When we updated the table of the confirmed exoplanets, we realized that this is the first Warm Neptunian of the confirmed exoplanets, another milestone.

Update#1: We modeled now a best case scenario using a mass-radius relationship that assumed an ocean planet and things changed a lot. Without mass it is very difficult to assess the habitability of Kepler-22 b. More observations will be needed to clarify its habitability status. It is so close to a transition point between superterrans and neptunians, but here it is, Kepler-22 b as a habitable planet.

This interpretation is for an oceanic planet with a thick cloud layer and no continents. It is hard to believe how an exoplanet will get so much water in the inner region of the snow line, but migrations are a possibility.

Update#2: The previous images shows two versions for Kepler-22 b, the worst case scenario as a superdense Warm Neptunian exoplanet and the best scenario as a habitable Warm Superterran ocean planet. It is hard to tell which version is correct and this only tell us that we need more observations of this exoplanet. We will evaluate it in more detail in the followings days to decide if it goes into the catalog.

Dec08: The paper for Kepler-22 b is now available in ArXiv but it briefly addressed its habitability. Probably a follow-up paper will do so. Also, the new Kepler candidates should be soon in the MAST Archives.

Update#1: The SPH of the picture above of Kepler-22 b, as an oceanic Warm Superterran, was updated. Although Kepler-22 b modeled surface temperature suggests a high SPH value, this is a habitability metric for land areas only and therefore zero for ocean planets (thanks to @andrewrushby for spotting this confusing value). Even an SPH for oceans exoplanets (now considering phytoplankton life instead of vegetation) will be zero or very low independently of temperature. Hereare some scientists opinions on the habitability of Kepler-22 b.

Here are a few transit simulations of Earth-like planets with and without moons (Figures 1-3) including Avatar's Pandora (Figure 4). All simulations assume long cadence observations (every 29.4 minutes) by the Kepler telescope and are stellar limb corrected. They were done with SPHERE-SIM, a software tool of the SPHERE Project to simulate complex transit events for statistical studies, such as those caused by multiple stars/planets, moons, and rings.

Figure 1. Animated simulation of the transit of Earth around the Sun as it will appear from far away to a Kepler-like telescope. The solid line is the expected stellar flux and the dots are the observed values, assuming a 40 ppm combined noise. Time is with respect of mid-transit. This simulation does not include the Moon. A MP4 movie version of this animation is also available.

Figure 2. Simulated stellar flux of the transit around the Sun of Earth alone (top) and Earth with the Moon (bottom) as it will appear from far away to a Kepler-like telescope. The blue curve is the expected flux and the red dots the observed flux, assuming a combined noise of 60 ppm. The presence of the Moon (at its maximum separation of 60 Earth radii) causes a small dent (starting at -10 hours) in the expected flux but this is not apparent in the observed flux.

Figure 3. Simulated stellar flux of the transit of Kepler-22 b alone (top) and with a hypothetical one third size moon (bottom). The blue curve is the expected flux and the red dots the observed flux, assuming a combined noise of 60 ppm. Even that the hypothetical moon (located at 20 Kepler-22 b radii) is a little larger than Mars (0.6 Earth radii) its presence is not easily notable in the observed flux.

Figure 4. Transit simulation of the fictional planet Polyphemus and its moon Pandora from the sci-fi movie Avatar. This is an example of a transit of a Saturn-size planet with a Venus-size moon around a Sun-like star. The relative size of the star, planet, and moon are shown in the top frame. The presence of a moon (bottom) is barely notable (starting around -20 hours) against the strong transit signal of the planet. Most of the planetary parameters used for this example are from Avatar: A Confidential Report on the Biological and Social History of Pandora. We already know that it is unlikely that a planet such as Polyphemus exist around Alpha Centauri A since we already have the capability to detect such large planets (sorry Jim). However, smaller Earth-size ones are still possible, such as Alpha Centauri B b.

Here are some quick stellar and planetary properties (Tables 1 and 2) for the three exoplanets system KOI-961 plus the basic habitability assessment with the Habitable Zone Distance (HZD) and Earth Similarity Index (ESI). This is the smallest system of exoplanets so far and the first three confirmed hot subterrans, between Mars and Earth size (this image will be updated soon). The exoplanets of KOI-691 are too close to their star for liquid water (HZD < -1) and not potentially habitable (ESI < 0.7). Check the HEC Top 10 for a list of other small exoplanets.

Table 2: Planetary properties of the three exoplanets around KOI-961. All are probably subterrans (mass between 0.1 to 0.5 Earth masses) orbiting in the hot zone of their parent star (the inner region outside the habitable zone).

Earth's atmospheric mass is about 5.3 x 1018 kg, that is close to one part per million (ppm) of its total mass. The atmosphere mass fraction of a planet can be estimated from its radius, mass, and surface pressure. This is assuming that the atmosphere is small compared to the total planet's mass. The fraction of atmospheric to planet mass is given by

where P is the mean surface pressure in bars, R is the radius and M the mass of the planet, both in Earth Units. The same equation can be used to get the fraction of each atmospheric component from their partial pressure. This fraction is shown for objects of the Solar System in Figure 1. The pressure of some gases in the atmosphere are limited by their condensation (e.g. water, carbon dioxide). As a reference, Figure 2 shows an atmospheric gas retention plot for hydrogen, nitrogen, and carbon dioxide.

Figure 2. Gas retention plot for hydrogen, nitrogen, and carbon dioxide for various Solar System objects. It shows escape velocity vs surface temperature. Earth and Venus are well within the hydrogen and nitrogen lines. Credit: University of Nebraska-Lincoln Astronomy Applets.

The equation can be used to estimate the potential surface pressure of Earth-like exoplanets given reasonable estimates of their atmosphere mass fraction. For example, Gliese 667Cc, has a minimum mass of 3.8 Earth masses which suggest a radius of 1.5 Earth radii assuming a rocky composition. If its atmosphere mass fraction is one ppm (just like Earth) then its surface pressure will be 3.3 bars. That is the pressure 23 meters below water, not that bad.

Thanks to Mario S. Garcíafor pointing out the error in the original equation.

This table summarizes in eighteen thermal-mass categories most of the current known exoplanets (as of October 2011). Planets are divided in six mass classes as mercurians, subterrans, terrans, superterrans, neptunians, and jovians. Planets in the hot zone (first row) are too close to the stars to support liquid water. Planets in the habitable zone (second row) can sustain liquid water if large enough. Planets in the cold zone (third row) are icy-rich bodies. The mean mass (M) and radius (R) of the exoplanets in each category is shown at the bottom of the frames.

In the Solar System Mercury is an example of a hot mercurian, Venus is on the edge of a hot and warm terran, Mars is on the edge of a warm subterran and mercurian, Jupiter and Saturn are cold jovians, and Uranus and Neptune cold neptunians. Only warm subterrans, terrans, and superterrans are potentially habitable, although warm jovians might have habitable exomoons. The only known mercurian was discovered in the Arecibo Observatory. You can click the image for a higher resolution version. An updated of this table will be available for the Habitable Exoplanets Catalog.

We evaluated the new release of 2740 NASA Kepler Candidates and identified 10 new candidates for potential habitable exoplanets from the previous batch. We also noticed that nine of the previous candidates do not qualify now. Therefore, the total did not change much and is now 30. The new candidates are: [KOI-3010.01], [KOI-2762.01], [KOI-172.02], KOI-1298.02, KOI-2834.01, [KOI-2931.01], KOI-518.03, KOI-3036.01, KOI-2882.01, KOI-581.02. Those four within brackets have a radius below 2 Earth radii. Only Kepler-22b (KOI-87.01) has been confirmed so far.

We barely have the capability to detect Earth-size exoplanets, less moons around them. Small exomoons will be atmosphere-less bodies, like our own Moon that shares with Earth the habitable zone (HZ). However, large exomoons are a very interesting target for astrobiology because they could be habitable if orbiting exoplanets in the HZ. They will be able to hold denser atmospheres, and liquid water, specially if farther away from the center of their HZ (Williams et al., 1997). Terrestrial-size habitable exomoons are more probable around gas giants as only larger planets can have larger moons, as the moon Pandora depicted in the movie Avatar. The good news is that we already have the capability to detect gas giants in the HZ.

There are some interesting relations between moons and planets masses if we use the Solar System as an example (Figure 1). Earth and Pluto are two exceptional cases, with very large moons relative to their size. Our Moon is 1.2 % and Charon is 13% of Earth and Pluto mass, respectively. However, the four giant planets have a similar moon-planet ratio of 1-3 x 10-4 (0.01-0.03%), a much smaller fraction. This is even true for Neptune, which acquired Triton after its formation. For comparison, the combined mass of the planets and moons are 0.13% of the Sun's mass. It seems that there is some deeper relation between the mass of the moons and the giant gas planets.

Figure 1. Moon to planet mass ratio for planets of the Solar System. The mass ratio between the planets and the Sun is shown for comparison.

Indee, Canup and Ward (2006) showed that the moon-planet mass fraction for the gas giants in our Solar System is probably the norm too for gas giant exoplanets. Although other process can bring exomoons to different sizes, they generally should be nearly 10-4 masses of their parent planet. This means that there are probably Moon to Mars size around gas giants. Ocean exomoons will generally be larger than rocky ones with the same mass. In the HZ they might be able to hold an atmosphere with liquid water surface for those with masses over 0.12 Earth masses (Williams et al., 1997). Exomoons are probably very abundant around gas giants but less likely for those orbiting very close together (Namouni, 2010).

Candidates for habitable exomoons have already been identified (Tinney et al., 2011). With new discoveries, including Kepler, results, there will be a need to catalog potential habitable exomoons sites. We need a simple relationship between a gas giant mass and their potential moons mass and radius. These properties are related to their habitability as they constrain the ability of the moon to hold an atmosphere in the HZ. Assuming exomoons with a high water fraction, a likely event for those orbiting gas giants, a simple relation can be derived from the 10-4 ratio and a mass-radius relationship for ocean worlds (Sotin et al., 2007) as

where mp is the mass of the gas giant exoplanet in Jupiter masses, mm and rm are the mass and radius of the exomoon in Earth's units, respectively. Figure 1 plots this relation for gas giants between 0.03 to 13 Jupiter masses. This analysis will be used as part of many other considerations that are needed to identify habitable exomoons sites for the Habitable Exoplanets Catalog.

Figure 2. Potential mass and radius of water-rich exomoons around gas giant exoplanets. Water-rich exomoons around giants over 10 Jupiter masses could approach Earth size. Those of rocky composition will be smaller. Exomoons in gas giants of more than 4 Jupiter masses in the habitable zone probably have atmosphere with ocean or mushy surfaces, a "melted Europa."

For more general discussions about exomoons, including direct detection methods, see:

Abel Mendezabel.mendez@upr.eduthemassandradiusofpotentialexomoons4https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/53494874270831880352014-10-02T09:27:09.740Z2016-08-24T16:48:50.515Z2014-10-06T22:21:55.286ZWe should prepare the map for the future space explorers

Here are two translations from a passage of an open letter from Kepler to Galileo published in the Conversation with the Star Messenger on April 19, 1610. We are still creating the maps of the universe for the future space explorers after four hundred years.

"There will certainly be no lack of human pioneers when we have mastered the art of flight. Who would have thought that navigation across the vast ocean is less dangerous and quieter than in the narrow, threatening gulfs of the Adriatic, or the Baltic, or the British straits? Let us create vessels and sails adjusted to the heavenly ether, and there will be plenty of people unafraid of the empty wastes. In the meantime, we shall prepare, for the brave sky-travellers, maps of the celestial bodies – I shall do it for the moon, you Galileo, for Jupiter." (1)

"But as soon as somebody demonstrates the art of flying, settlers from our species of man will not be lacking. Who would once have thought that the crossing of the wide ocean was calmer and safer than of the narrow Adriatic Sea, Baltic Sea, or English Channel? Given ships or sails adapted to the breezes of heaven, there will be those who will not shrink from even that vast expanse. Therefore, for the sake of those who, as it were, will presently be on hand to attempt this voyage, let us establish the astronomy, Galileo, you of Jupiter, and me of the moon." (2)

Abel Mendezabel.mendez@upr.eduthemaps10https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/15119984253007466742014-10-06T22:00:04.290Z2016-08-24T16:48:50.514Z2014-10-06T22:23:16.398ZThe Map to the Stars

"There will certainly be no lack of human pioneers when we have mastered the art of flight ...

In the meantime, we shall prepare, for the brave sky-travellers, maps of the celestial bodies."

This is a map of the over one thousand stellar systems with known exoplanets. The map helps to visualize the relative distance and location of exoplanets systems with respect to Earth using a flattened polar projection (i.e. zero declination) with a logarithmic distance scale. Those systems with potentially habitable exoplanets are highlighted with a red circle. You will need to enlarge to see details (probably something good for a Prezi presentation).The map can be printed 27" x 27" @ 300dpi. Check the original poster from 2011 for comparison.

Kepler-16 (AB) b, aka "Tatooine," is the first exoplanet detected around binary stars (Doyle et al., 2011). The planet has a mass and size comparable to Saturn but orbits the star system with a period and distance similar to Venus. Its parent binary system is fainter than the Sun therefore making the planet colder than Mars instead of a hot desert as suggested by its colloquial name. In any case, Kepler-16 (AB) b is probably a gas giant and not suitable for life. However, it lies in the outer edge of the habitable zone (HZ) and its moons, if any, could be habitable if large enough to hold a dense atmosphere like Titan does precisely on Saturn.

Here we calculated the HZ for all the 684 confirmed planets so far from the Extrasolar Planets Encyclopedia (Figure 1). We used the Habitable Zone Distance (HZD) habitability metrics as a measure of the planet location with respect to its parent star HZ. Planets in the middle of the HZ have a HZD of zero while minus or plus one in the edges, depending if they are closer or farther from the star, respectively. Planets in the HZ are only considered habitable if they have a terrestrial-like size. Smaller ones will not be able to hold an atmosphere (i.e. look at our Moon right next to us in the habitable zone) while gas giants will have crushing pressures. Kepler-16 (AB) b is in the cold side of the HZ.

A moons mass scaling (Canup and Ward, 2006) analysis suggest that any Kepler-16 (AB) blargest moons are probably around 0.01 Earth masses, a size of 0.3 Earth radii assuming a mass-radius relationship for ocean bodies (Sotin et al., 2007). That is comparable to the size of our own Moon or Io. Any such moons will be a barren world closer to the star systems but at their distance it is plausible to have an atmosphere. Unfortunately, they will probably be a Mars-cold environments. Only the presence of much larger moons will allow for a habitable environment. Another more interesting possibility is an oceanic tidal-heated hot-Europa moon.

Our calculation for the HZ of Kepler-16 (AB) b only considered the main star and ignored the colder contribution of the secondary binary. Therefore, we expect that Kepler-16 (AB) b is actually a little bit closer to the center of the HZ but still a cold world. The dynamic nature of its HZ will be later explored but we do not expect large variations because the binary system is close together and the contribution of the secondary star is smaller even considering its higher emission in the infrared.

Figure 1. Comparison of the habitable zone (HZ) using the Habitable Zone Distance (HZD) habitability metrics for 684 confirmed exoplanets (red) with Solar System planets (blue). The HZD provides a simple way to compare and assess the HZ for many exoplanets using Habitable Zone Units (HZU) with those within the green shade inside it (-1 to +1 HZU). The Solar System, Gliese 581, HD 85512 b, and Kepler-16 (AB) b planets are labeled (outer Solar System planets are out of the scale in the Cold Zone). Only 439 of the 684 exoplanets in the database had enough data to calculate the HZD. Most fall between the -3 to +3 HZU range. Of those, 305 fall in the Hot Zone (a detection bias), 52 in the Cold Zone, and 82 in the HZ. Kepler-16 (AB) b has a HZD = 0.6 HZU which puts it in a worst position than Mars but similar to Gl 581 d, a potential habitable exoplanet.

We are developing a code to automatically generate updated diagrams and visualizations from various exoplanets catalogs for the Habitable Exoplanet Catalog. Here is a test showing the mass, temperature, and luminosity relationships of the 562 parent stars of the latest 684 exoplanets from the Extrasolar Planets Encyclopedia. All plots show the number of each spectral type in parenthesis. The sampled population is biased toward Sun like G stars although about 72% of stars are M stars (red dwarfs). High resolution versions of these plots are available on request for posters or presentations.

We will be doing a simple habitability analysis of Earth in the last 750 million years as part of the Visible Paleo-Earth (VPE) project. We are using the fossil record from the Paleobiology Database to visualize the global distribution of mayor life forms of the ancient Earth. The fossil record is very fragmented both spatially and temporally, but it gives a general idea of the suitability for life of past terrestrial environments. Here are two test visualizations for the Early Cretaceous Period (120 Ma) with the occurrence locations for animals and plants (both terrestrial and marine records). The modern map (Fig. 1) shows the location of the fossil excavation sites while the 120 Ma map (Fig. 2) shows their past location. The actual shown fossil data corresponds to the time intervals between 130 to 110 Ma so their location is just an estimate for 120 Ma. The habitability analysis will be discussed in a later post including the visualization for all the periods in the VPE.

Figure 1. Excavation location of the fossil record of the Early Cretaceous Period (120 Ma) for animals and plants (terrestrial and marine). Data from the Paleobiology Database.

Figure 2. General location of animals and plants (terrestrial and marine) based on the fossil record during the Early Cretaceous Period (120 Ma). Data from the Paleobiology Database.

Abel Mendezabel.mendez@upr.edutheglobalpaleo-distributionoflife11https://sites.google.com/feeds/content/upr.edu/planetary-habitability-laboratory-upra/86688835436447896942011-06-07T07:24:43.379Z2016-08-24T16:48:50.512Z2012-07-02T02:19:40.458ZThe Distribution of Complex Life in the Last 540 Million Years

Following our previous post for the paleo-distribution of life, here we show two animations of the distribution of complex life in the last 540 million years based on the fossil record, starting from the Cambrian Period to today. This was the period when life became complex and populated the continents (Figure 1). The fossil record is very limited and fragmented both spatially and temporally, but the animations gives a general idea of how life evolved and shifted through space and time.

Figure 1. Timeline of the last 700 million years of Earth.

The animations show the fossil record for ten well known taxa: mammalia, reptilia, dinosauria, insecta, avialae, pisces, amphibia, trilobita, ammonoidea, and plantae. The data came from the Paleobiology Database and it is being used together with the Visible Paleo-Earth in a comparative analysis of terrestrial habitability for those periods. The animations were georeferenced for today coordinates, where the fossils were found (Figure 2), and for the paleo-coordinates, where the taxa was living (Figure 3). Note that many of the fossil occurrence sites overlap and it is always better to see each taxon alone to appreciate its distribution.

Figure 2. These are the locations of fossil sites for 25 geological periods from 540 million years ago to today.

Figure 3. This animation shows the distribution of complex life in the last 540 million years based on the fossil record.